Reports on adolescent populations outside the U.S. indicate a wide variation in the prevalence of periodontal diseases. The purpose of this cross-sectional study is to determine the prevalence of gingivitis, epithelial attachment loss, and bone loss in a group of adolescents residing in the U.S. The study population consisted of approximately 600 Navajos, ages 14-19 years. Twenty-four posterior interproximal sites were examined on each subject. Gingivitis was assessed using a modification of the G.I. Loss of attachment was assessed using Ramfjord's technique. Bone loss was diagnosed from standardized bitewing radiographs. Several FORTRAN programs were written to analyze the clinical data. Preliminary analyses indicate a high prevalence of disease: gingivitis, (71%); attachment loss, (89%); and bone loss, (89%). The average number of sites in the mouth affected with the more advanced form of disease (attachment loss and bone loss) was also high: 32% of the sites had attachment loss, and 22% had bone loss. More detailed analyses are being done, and all research findings will be submitted for publication by Spring 1986. A longitudinal study is planned with the youngest subjects to investigte microbiologic, systemic and other factors that may contribute to the high prevalence of disease.